Middle Irish (900-1200)
The standard of Old Irish declined in the Middle Irish period, although no indication of dialect formation is as yet evident. There is uncertainty in morphology as writers were less sure just what constituted classical Old Irish. The period drew to a close with the coming of the Normans at the end of the 12th century in the south-east of the country.
The simplification of the inflectional system continued throughout the Middle Irish period with the nominal and verbal system of Old Irish much reduced (Dottin 1913). By the end of the Middle Irish period there is no distinction between genitive and dative with most nouns and the complex system of verb prefixes has been greatly simplified either by these being dropped or by being absorbed into the stem of a verb and becoming opaque as a result.
Independent forms of personal pronouns develop during this period. The old infixed pronouns are replaced by post-posed independent pronouns. Synthetic forms of pronoun and copula are replaced by an invariable form of the copula with generic personal pronouns.
Changes in the sound system led to certain realignments. The loss of /θ/ and /ð/ – probably in the 13th century, O’Rahilly (1926) – resulted in different outcomes for lenition as an initial mutation. S became /h/ and D became ɣ on lenition.
There is no contemporary handbook of Middle Irish, although there is an older work by Georges Dottin from 1913 (second image below). The best treatment of this stage of the language is probably the following long article in Stair na Gaeilge :
Breatnach, Liam 1994. ‘An Mheán-Ghaeilge’ [Middle Irish], in: McCone, Kim, Damian McManus, Cathal Ó Háinle, Nicholas Williams and Liam Breatnach (eds) 1994. Stair na Gaeilge. In Ómós de Pádraig Ó Fiannachta [The History of Irish. In Honour of Pádraig Ó Fiannachta]. Maynooth: Department of Irish, pp. 221-334.